Why are BeH2 and MgH2 polymeric in structure? Plz explain. Plz show the structure also.

hi,

. The hydrides of beryllium and magnesium are covalent and polymeric (BeH2)n. has a chain structure containing chains with hydrogen bridges between beryllium atoms
Each beryllium atom is bonded to two hydrogen atoms and each hydrogen atom to two beryllium atoms. Now, beryllium has only two valence electrons and hydrogen only one, it is apparent that there are not sufficient electrons to form so many electron pair bonds. The monomeric BeH2, if formed with normal bonds, would have only four electrons in the valence shell of the beryllium atom and would be electron deficient and unstable. It polymerizes to remedy the electron deficiency. The bonds formed cannot be explained by the classical theories of bonding. They are “banana shaped” molecular orbitals holding three atoms Be ---- H ---- Be together and are called 3 centred – 2- electron (3c – 2e) bonds. It is an example of a cluster compound.

 

The hydrides of beryllium and magnesium are covalent and polymeric (BeH2)n. has a chain structure containing chains with hydrogen bridges between beryllium atoms Each beryllium atom is bonded to two hydrogen atoms and each hydrogen atom to two beryllium atoms. Now, beryllium has only two valence electrons and hydrogen only one, it is apparent that there are not sufficient electrons to form so many electron pair bonds. The monomeric BeH2, if formed with normal bonds, would have only four electrons in the valence shell of the beryllium atom and would be electron deficient and unstable. It polymerizes to remedy the electron deficiency. The bonds formed cannot be explained by the classical theories of bonding. They are “banana shaped” molecular orbitals holding three atoms Be ---- H ---- Be together and are called 3 centred – 2- electron (3c – 2e) bonds. It is an example of a cluster compound.